How Ball Bearings Are Made

Round objects, like ball bearings, have always been used to make jobs easier. There are many types of rolling bearings that also come in a wide variety of sizes. Most commonly, ball bearings can be held in the palm of your hand.

When examining how ball bearings are made, we must first look at the materials used. Most ball bearings are made of steel. This material is used due to its tolerance to stress. To achieve the necessary industry standards, steel used for ball bearings may be hardened or made tougher using heat treatment. While some newer bearings now use molded plastic cages for cost reasons, many cages are traditionally formed from thin steel.

The manufacturing process for ball bearings can be broken down to four components: the outer race, inner race, rolling balls and cage formation.

1-2. Races

Both the inner and outer races are made using a similar process. Starting with steel tubing, machine cutting tools cut the tubing slightly larger than the race shape. The cut is made larger to allow for shrinking during the heat treatment where the furnace is set to approximately 1,550 degrees Fahrenheit. After the rough cut race has spent several hours in the furnace, it is dipped into an oil bath to cool and harden. After the heat treatment process is complete, the races are finished by using grinding wheels to achieve the final smooth surface.

3. Balls

A more difficult process than forming the races, the balls are made starting with thick wire. Fed from a coil of raw material, the wire then goes through the cold heading process. Through this process, a bulge at the centerline of the ball is formed which needs to be removed. The balls are then transferred into grooves that sit between one rotating and one stationary cast iron disc. The friction created then removes the flash/bulge. Throughout this entire process the balls are left slightly oversized to account for heat treatment. Similar to the races heat treatment, the balls are hardened and made tough. Following heat treatment, the balls are put back into a similar process between the two discs accept now the wheels are grinding wheels, not cutting wheels, taking the balls within a few ten thousandths of an inch of the final size. The balls are moved to the lapping machine where cast iron wheels use an abrasive lapping compound to finish the ball.

4. Cage

The cages are made by stamping thin sheet metal, similar to using a cookie cutter. After the initial cut, the cage is bent to the desired final shape using a die. Plastic cages are made differently using a process called injection molding. This process begins with the mold that is then injected with the melted plastic which is allowed to harden.

After the parts are made, the ball bearing is ready to be assembled. To begin, the inner race is put inside the outer race, leaving space to insert the ball between the two. After inserting the number of balls necessary, the races are then centered and the balls are distributed evenly. Finally, the cage can be installed to hold the balls apart.

As with any manufactured product, after assembly, each part goes through quality control. Simple and easy to manufacture, ball bearings will continue to be a popular component well into the future.